Rotary drilling bit



P 8, 1936- w. J. MITCHELL 2,053,801

I I ROTARY DRILLING BIT Filed May 29, 1934 Willin limii h tll Patented Sept. 8, 1936 PATENT OFFICE ROTARY DRILLING BIT William J. Mitchell, San Francisco, Calif., as-

signor to Chicago Pneumatic Tool Company, New York, N. Y., a corporation of New Jersey Application May 29, 1934, Serial No. 728,114

4 Claims. (Cl. 25561) My present invention relates to an improved rotary drilling bit of the core type, which bit while adapted for use in various ways, is especially designed for drilling blasting-holes employed in different forms of excavation work. The primary object of the invention is the provision of a highspeed rotary drill bit on which the diamond-cutters or stones are arranged in such manner as to insure maximum durability for the cutters with which the face of the bit is studded, and also to assure maximum efliciency for the bit in the performance of its functions of earth drilling or boring. 1

The invention consists essentially in certain novel combinations andarrangements involving a bit having a threaded collar for attachment to the tubular drill-rod of a drilling machine, and in the hollow bit-head with its cutting-face and cutters located thereon, as will hereinafter be more fully set forth and claimed. In the accompanying drawing I have illustrated several forms of the invention, in which the bit is adapted for work in both hard and soft earth where excavations are to be made, but it will be understood that changes and alterations may be made in these exemplifying structures, within the scope of my claims without departing from the principles of my invention.

Figure 1 is a side view of a bit embodying my invention, with the cutting stones or diamonds omitted for convenience of illustration; and Figure 2 is an enlarged detail sectional view of the bit.

Figure 3 is a sectional view of a high speed bit adapted specially for use in comparatively soft earth, and involving my invention; and Figure 4 is a face of the bit of Figure 3.

Figure 5 is a side view of another form of bit involving my invention, with the diamonds omitted; and Figure 6 is an enlarged detail sectional view of the bit of Figure 5 showing the replaceable orinterchangeable cutter-holder at the center of the bit.

In the form of the invention shown in Figures 1 and 2 the bit is adapted for boring or drilling in hard stone, granite and other hard materials; in Figures 3 and 4 the bit is especially adapted for boring or drilling in limestone, sandstone, and other soft stones, as well as in soft-earth; and in the bit of Figures 5 and 6 I illustrate particularly a removable and replaceable cutter holder by means of which the durability and usefulness of the bit is prolonged.

In all forms of the bit illustrated I employ a substantially rounded or convex head I having an integral, exterlorly threaded collar 2 by means of which the bit is threaded on the end of the usual tubular drill rod of a drilling machine. The front face 3 of the head is rounded or convexed, but not pointed, and the central portion of the face of the head is flattened or truncated. The head is hollow and is provided with an interior, comparatively large water chamber 4, which receives water under pressure from the tubular drill rod, and by means of the distributing ports 5 that open to the cutting face of the bit, water is fed in front of the rotating bit, for the purpose of carrying off the cuttings or dbris. These cuttings are subsequently disposed of and conveyed to the surface of the ground by the water flowing back through the drilled-hole around the outside of the tubular drill rod.

The central cylindrical water chamber 4 is also open to the cutting face of the bit through a central port 6, which is countersunk or enlarged at l where it opens into the water chamber 4. During the cutting operations an uncut core is fashioned at the center of the bottom of the drilled-hole. This core, if fashioned from soft earth or other soft material, is quickly broken into small particles which are scattered by the passage of the water under pressure to the face of the bit; if the bit is working in hard material, as granite, the uncut core may enter the central port 6 of the bit before being disintegrated, but

the core is eventually crushed or broken into small bits which may be conveyed by the water under pressure through the several outlet ports for water, through and from the interior of the hollow bit.

In the bit illustrated in Figures 1 and 2, which is especially adapted for drilling in hard rock, the flattened convex face of the head is provided with an inverted, cone-shaped recess 8, the annular wall of which flares outwardly from the central port 6 of the bit, and the wall of the recess merges with the face of the bit to form an annular shoulder between the convex portion and the concave portion of the face, as best seen in or revolves.

I have found by actual practice that if cutters are located at the apex or central part of the convex face of the bit, these cutters bear the brunt of pressure applied to the bit, and, although these cutters turn at a slower surface speed than the cutters located at a distance from the center of the bit, the central cutters wear away more rapidly than the cutters having the greater surface speed. Therefore, by dispensing with the use of cutters at the center 'of the bit, the remaining cutters or diamonds, having a more uniformly faster surface speed, bear the brunt of the pressure, and the pressure is thus more evenly distributed for more nearly uniform wear on the cutters.

The presence of the depressed recess or concave face in the convex bit-face, also-serves, with the convex face, to maintain the true course of the advancing bit as it is fed to its work.

In Figures 3 and 4 where the illustrated bit is designed to penetrate comparatively soft material, the high speed of the rotary bit and rapid cutting of the soft material, require a larger clearance space to accommodate the rapidly formed cuttings, and these cutting are disposed of through the series of radial grooves I which extend from a point adjacent the central port 6 to the outer edge of the bit.

In Figures 5 and 6 I illustrate the use of a removable cutter-holder or tubular insert I I having the water chamber 4, the central port 6 and countersunk hole I, and a recess 8' similar to the recess of Figure 2. This tubular cutter-holder may readily be fitted into the hollow bit, or removed therefrom when the cutters 9 on the face 8' become worn, and fresh cutters may be substituted for the worn cutters, or another holder with fresh cutters may be substituted for the used holder. The holder is of substantially cylindrical form or shape, and its inner, threaded end protrudes through the rear end of the bit to receive a fastening nut 12 that is turned tight against the face of the collar 2, and the latter is attached as usual to the tubular drill rod.

The front end I3 of the tubular holder is tapered, and flares outwardly ahead of the main cutting face of the bit, in order that the nut may draw the holder tightly into the hollow head to insure that the rigidly connected bit and holder may revolve or rotate together.

From the water chamber 4 of the holder, the water passes through one or more lateral ports it into an annular space or water chamber I5 of the bit-head, and from thence the water flows to the exterior of the bit through the ports 5. The holder is also provided with the central opening 6-! to take care of the core that is formed, or may be formed in the bottom of the drilled-hole, and to supply water to the cutters or diamonds in the face of the recess 8'. Should these cutters wear away more rapidly than the cutters on the convex face of the head of the bit, another holder may readily be substituted.

Having thus fully described my invention, what I claim as new and desire to secure by Letters Patent is:

l. A hollow drilling-bit having a front opening. a tubular cutter-holder having a front opening and means for securing said holder in the bit, said cutter-holder having a concave cutting face surrounding its front opening, a convex cutting face on the bit surrounding the holder, cutters set in said faces, and means for attachment to a tubular drill rod.

2. A hollow drilling bit having a front opening, a convex cutting face surrounding said opening, and cutters in said face, a removable, tubular cutter-holder having a threaded end and located in the bit and a securing nut on said threaded end, another end of said holder having an outwardly flaring head of greater diameter than the diameter of the hollow drilling bit, said flaring head having a concave cutting face surrounding a central front opening of the flaring head and cutters in said face, and means for attachment to a tubular drill rod.

3. A hollow drilling bit having a central opening terminating in a reduced orifice, a concave cutting face surrounding the outer end of the orifice, a convex cutting face surrounding said concave cutting face and outlet ports from the interior of the bit to said convex face, cutters set in said faces, and means for attaching the drilling bit to a tubular drill rod.

4. A hollow drilling bit, a tubular cutter-holder having an exterior head portion, and means for securing said holder in the bit, the interior of said tubular holder terminating in an orifice in its head-portion, a concave cutting face in said head portion surrounding the orifice, a convex cutting face on the bit surrounding the head- 'portion, cutters set in said faces, and means for attaching the bit to a tubular drill rod.

WILLIAM J. MITCHELL. 

